1. Field of Invention
The invention relates to a rotary feed-through.
2. Prior Art
Such rotary feed-throughs are used to supply fluid to a rotating machine part. In particular, with machine tools, such rotary feed-throughs are used to feed a cooling lubricant into a hollow working spindle of the machine tool for cooling or cleaning tools and/or the work point. For typical rotary feed-throughs, the interface between the rotating and the stationary part is formed by sealed bushings or sealing rings with sealing surfaces sliding one on top of the other. For the supply of a lubricant medium, such as, e.g., cooling lubricant, the sealing gap between the two sliding surfaces is lubricated, which prevents too high a temperature load and too much wear and tear. However, there are also applications for which a non-lubricating medium must be supplied. Thus, for certain applications, e.g., a supply of compressed air for cooling the tool and/or workpiece or also for removing shavings is necessary. However, here there is the problem that the resulting lack of lubrication on the sliding surface leads to an increased build-up of heat and increased wear and tear.
From DE 199 32 355 A1, a rotary feed-through according to this class is known for alternating media. However, in this document, the sealing surfaces are only in contact when a lubricating medium is supplied. For the supply of a non-lubricating medium, the sealing surfaces are moved away from each other in order to prevent too much wear and tear on the sealing surfaces. In order to minimize the resulting leakage losses, there is an additional cylindrical seal in the form of a sealing gap between the outer wall of a rotationally fixed sleeve and the inner wall of a hollow shaft.
For another type of rotary feed-through, the problem of lubrication and cooling of the sliding surfaces is solved by supplying the sealing elements, which slide one on top of the other, with an additional coolant or lubricant from the outside. However, this requires constructional expense that is not insignificant, because the additional coolant and lubricant must be constantly supplied and discharged for continuous dissipation of the frictional heat.